Does stress affect elephant fertility?

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Endangered Asian elephants age faster and have fewer offspring if their mothers are stressed when they are born.By measuring chemical markers of stress present in elephant dung, a research team at the University of Sheffield, led by Hannah Mumby, was able to determine the most stressful time of year for these elephants.

Comparing this data with a unique, long-term record of Burmese Asian elephant births enabled the scientists to study the influence of ageing and stress on the animals' fertility.

According to Mumby, "the elephants have been tracked very closely, so we have complete life history data on about 8,000 elephants and up to five generations."

The Asian elephants that were studied are working, semi-captive elephants that are used in the timber industry moving logs.

Samples were taken from the elephants for a whole year to monitor stress levels. The monsoon season, from July to October, emerged as the most stressful time, associated as it was with increased maternal work-load and higher disease prevalence.

The results, which were published in Scientific Reports earlier this week, show that the elephants born in this "stressful" season produce more offspring when they are younger, but hardly produce any offspring later in life. This pattern is very different compared with elephants born in the other seasons.

Mumby explains that, unlike humans, elephants do not experience a menopause as such. "At the start everything looks very similar between humans and elephants; but in humans, where you hit this wall of menopause and no one reproduces after that, what elephants experience is more of a slow decline."

The factors that contribute to differences in reproductive ageing in long-lived species are becoming more and more important as the age at which modern women want to have children is increasing.

By studying the subtle differences in effects of environment, and the mortality and fertility rates of these endangered Asian elephants, this can give a better understanding of how we can tackle the declining numbers of the animals both in captivity and the wild.